Method and apparatus for performing handover in a next-generation communication system

ABSTRACT

The disclosure relates to a 5G or pre-5G communication system for supporting a data transmission rate higher than a 4G communication system such as LTE. A method performed by a UE in a communication system includes: receiving, from a base station associated with NR, a command message for inter-RAT handover from the NR to a target RAT, wherein the command message includes information on a type of the target RAT; performing a procedure associated with the inter-RAT handover based on the command message; in case that a failure condition for the inter-RAT handover is satisfied, identifying that the inter-RAT handover fails; and in case that the type of the target RAT is set to EUTRA and the UE supports a radio link failure report for inter-RAT MRO EUTRA, storing handover failure information in a variable for the radio link failure report based on an identification that the inter-RAT handover fails.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. § 119to Korean Patent Application No. 10-2020-0183060, filed on Dec. 24,2020, in the Korean Intellectual Property Office, the disclosure ofwhich is herein incorporated by reference in its entirety.

BACKGROUND 1. Field

The disclosure relates to an operation of a user equipment (UE) and abase station in a next generation mobile communication system.Particularly, the disclosure relates to an inter-radio access technology(RAT) handover and an intra-RAT handover in a next generation mobilecommunication system.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

Discussion on a method for a UE to perform handover is being conductedin order to efficiently implement a communication system in theabove-described 5G system.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

An aspect of the disclosure is to provide a method of overcomingdrawbacks which may occur when a handover is performed. Particularly,there is provided a method of overcoming drawbacks which may occur whenan inter-radio access technology (RAT) handover or an intra-RAT handoveris successfully performed or fails.

According to an embodiment of the disclosure, a method performed by auser equipment (UE) in a communication system is provided. The methodincluding: receiving, from a base station associated with newradio-radio access (NR), a command message for inter-radio accesstechnology (RAT) handover from the NR to a target RAT, wherein thecommand message includes information on a type of the target RAT;performing a procedure associated with the inter-RAT handover based onthe command message; in case that a failure condition for the inter-RAThandover is satisfied, identifying that the inter-RAT handover fails;and in case that the type of the target RAT is set to evolved universalterrestrial radio access (EUTRA) and the UE supports a radio linkfailure report for inter-RAT mobility robustness optimization (MRO)EUTRA, storing handover failure information in a variable for the radiolink failure report based on an identification that the inter-RAThandover fails.

According to an embodiment of the disclosure, a UE in a communicationsystem is provided. The UE comprises: a transceiver; and a controlleroperably coupled to the transceiver, and configured to: receive, from abase station associated with NR via the transceiver, a command messagefor inter-RAT handover from the NR to a target RAT, wherein the commandmessage includes information on a type of the target RAT, perform aprocedure associated with the inter-RAT handover based on the commandmessage, in case that a failure condition for the inter-RAT handover issatisfied, identify that the inter-RAT handover fails, and in case thatthe type of the target RAT is set to EUTRA and the UE supports a radiolink failure report for inter-RAT mobility MRO EUTRA, store handoverfailure information in a variable for the radio link failure reportbased on an identification that the inter-RAT handover fails.

According to various embodiments of the disclosure, there is provided amethod of overcoming drawbacks which may occur when an inter-radioaccess technology (RAT) handover or an intra-RAT handover issuccessfully performed or fails.

According to an embodiment of the disclosure, there is provided a methodof processing a timer of a user equipment (UE) which successfullyperforms an inter-RAT handover, and the UE is capable of appropriatelyperforming a logged minimization of drive test (MDT) operation.

In addition, according to an embodiment of the disclosure, there isprovided a method of storing handover failure information associatedwith a UE if an inter-RAT handover fails, and thus, an efficientcommunication system may be implemented.

In addition, according to an embodiment of the disclosure, there isprovided a method of storing handover failure information associatedwith a UE if an intra-RAT handover fails, and thus, an efficientcommunication system may be implemented.

Effects that could be obtained based on the disclosure are not limitedto the above-described effects, and those skilled in the art would beclearly understand, based on the descriptions provided below, othereffects which are not mentioned above.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure and its advantages,reference is now made to the following description taken in conjunctionwith the accompanying drawings, in which like reference numeralsrepresent like parts:

FIG. 1 is a diagram illustrating the structure of a next generationmobile communication system according to an embodiment of the presentdisclosure;

FIG. 2 is a diagram illustrating the structure of a radio protocol of anext generation mobile communication system according to an embodimentof the present disclosure;

FIG. 3 is a diagram illustrating technology that collects and reportscell measurement information according to an embodiment of the presentdisclosure;

FIG. 4 is a diagram illustrating a process in which a UE performshandover according to an embodiment of the present disclosure;

FIG. 5 is a diagram illustrating a process in which a UE performshandover according to an embodiment of the present disclosure;

FIG. 6 is a diagram illustrating a process in which a UE performshandover according to an embodiment of the present disclosure;

FIG. 7 is a diagram illustrating a process of storing handover failureinformation when a UE fails to perform handover according to anembodiment of the present disclosure;

FIG. 8 is a diagram illustrating a process of storing handover failureinformation when a UE fails to perform handover according to anembodiment of the present disclosure;

FIG. 9 is a diagram illustrating a process of storing handover failureinformation when a UE fails to perform handover according to anembodiment of the present disclosure;

FIG. 10 is a block diagram illustrating the structure of a UE accordingto an embodiment of the present disclosure; and

FIG. 11 is a block diagram illustrating the structure of a base stationaccording to an embodiment of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 11, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device.

Hereinafter, the operation principle of the disclosure will be describedin detail with reference to the accompanying drawings. In the followingdescription of the disclosure, a detailed description of known functionsor configurations incorporated herein will be omitted when it isdetermined that the description may make the subject matter of thedisclosure unnecessarily unclear. The terms which will be describedbelow are terms defined in consideration of the functions in thedisclosure, and may be different according to users, intentions of theusers, or customs. Therefore, the definitions of the terms should bemade based on the contents throughout the specification.

Hereinafter, various embodiments of the disclosure will be described indetail with reference to the accompanying drawings.

In the following description, terms for identifying access nodes, termsreferring to network entities, terms referring to messages, termsreferring to interfaces between network entities, terms referring tovarious identification information, and the like are illustratively usedfor the sake of convenience. Therefore, the disclosure is not limited bythe terms as used below, and other terms referring to subjects havingequivalent technical meanings may be used.

In the following description, the disclosure will be described usingterms and names defined in the 3rd generation partnership project longterm evolution (3GPP LTE) standards for the convenience of description.However, the disclosure is not limited by these terms and names, and maybe applied in the same way to systems that conform other standards. Inthe disclosure, the term “eNB” may be interchangeably used with the term“gNB.” That is, a base station described as “eNB” may indicate “gNB.”

FIG. 1 is a diagram illustrating the structure of a next generationmobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 1, as described in the drawing, a radio access networkof a next generation mobile communication system (hereinafter, NR or 5G)may include a next generation base station (a new radio node B(hereinafter, an NR gNB or an NR base station)) 1-10 and a new radiocore network (NR CN) 1-05. A new radio user equipment (NR UE) (or a UE)1-15 may access an external network via an NR gNB 1-10 and an NR CN1-05.

In FIG. 1, the NR gNB 1-10 corresponds to an evolved nodeB (eNB) of alegacy LTE system. The NR gNB is connected to the NR UE 1-15 via awireless channel, and may provide a better service than a service from alegacy NodeB. In the next generation mobile communication system, alluser traffic is serviced via a shared channel. Accordingly, there is adesire for a device that performs scheduling by collecting stateinformation such as buffer states, available transmission power states,channel conditions, and the like in association with UEs. The NR NB 1-10takes charge of the same. A single NR gNB generally controls a pluralityof cells.

In order to implement ultra-high speed data transmission when comparedto legacy LTE, a bandwidth greater than or equal to the current maximumbandwidth may be used, and an orthogonal frequency division multiplexing(OFDM) is used as a radio access technology and a beamforming technologyis additionally used. In addition, an adaptive modulation and coding(AMC) scheme that determines a modulation scheme and a channel codingrate may be applied based on the channel state of a UE. The NR CN 1-05performs a function of supporting mobility, configuring a bearer,configuration a quality of service (QoS), and the like. The NR CN is adevice that is in charge of various control functions in addition to amobility management function associated with a UE, and may be connectedto a plurality of base stations. In addition, the next generation mobilecommunication system may also interoperate with a legacy LTE system, andan NR CN is connected to a mobility management entity (MME) 1-25 via anetwork interface. The MME is connected to an eNB 1-30 which is a legacybase station.

FIG. 2 is a diagram illustrating the structure of a radio protocol of anext generation mobile communication system according to an embodimentof the present disclosure.

Referring to FIG. 2, the radio protocol of the next generation mobilecommunication system may include an NR service data adaptation protocol(SDAP) 2-01 and 2-45, an NR packet data convergence protocol (PDCP) 2-05and 2-40, an NR radio link control (RLC) 2-10 and 2-35, and an NR mediumaccess control (MAC) 2-15 and 2-30 for each of a UE and an NR gNB.

The main functions of the NR SDAP 2-01 and 2-45 may include some of thefollowing functions:

-   -   Transfer of user data (transfer or user plane data);    -   Mapping between a QoS flow and a data bearer (DRB) for both        downlink and uplink (mapping between a QoS flow and a DRB for        both DL and UL);    -   Marking a QoS flow ID in both a DL and an UL (marking QoS flow        ID in both DL and UL packets); and/or    -   Mapping reflective QoS flow to a data bearer for uplink SDAP        PDUs (reflective QoS flow to DRB mapping for uplink SDAP PDUs).

In association with an SDAP layer, whether to use the header of the SDAPlayer or whether to use the function of the SDAP layer may be configuredfor the UE via an RRC message for each PDCP layer, for each bearer, orfor each logical channel. If the SDAP header is configured, a NASreflective QoS configuration one-bit indicator (NAS reflective QoS) andan AS reflective QoS configuration one-bit indicator (AS reflective QoS)of the SDAP header may provide an indication so that the UE updates orreconfigures mapping information between a QoS flow and a data bearer inan uplink and a downlink. The SDAP header may include QoS flow IDinformation indicating QoS. The QoS information may be used as dataprocessing priority information, scheduling information, or the like forsupporting a smooth service.

The main functions of the NR PDCP 2-05 and 2-40 may include some of thefollowing functions:

-   -   Header compression and decompression: (header compression and        decompression: ROHC only);    -   Transfer of user data;    -   Sequential transfer (in-sequence delivery of upper layer PDUs);    -   Non-sequential transfer (out-of-sequence delivery of upper layer        PDUs);    -   Reordering (PDCP PDU reordering for reception);    -   Duplicate detection (duplicate detection of lower layer SDUs);    -   Retransmission (retransmission of PDCP SDUs);    -   Ciphering and deciphering; and/or    -   Timer-based SDU discard (timer-based SDU discard in uplink).

The reordering function of the NR PDCP device may refer to a function ofsequentially reordering PDCP PDUs received from a lower layer accordingto a PDCP sequence number (SN), and may include a function oftransferring sequentially reordered data to a higher layer, a functionof immediately transferring data irrespective of a sequence, a functionof recording lost PDCP PDUs after sequential recording, a function ofreporting the states of lost PDCP PDUs to a transmission side, and afunction of requesting retransmission of lost PDCP PDUs.

The main functions of the NR RLC 2-10 and 2-35 may include some of thefollowing functions:

-   -   Transfer of data (transfer of upper layer PDUs);    -   Sequential transfer (in-sequence delivery of upper layer PDUs);    -   Non-sequential transfer (out-of-sequence delivery of upper layer        PDUs);    -   ARQ (error correcting through ARQ);    -   Concatenation, segmentation, and reassembly (concatenation,        segmentation and reassembly of RLC SDUs);    -   Re-segmentation (re-segmentation of RLC data PDUs);    -   Reordering (reordering of RLC data PDUs);    -   Duplicate detection;    -   Error detection (protocol error detection);    -   RLC SDU discard; and/or    -   RLC re-establishment.

The mentioned in-sequence delivery function of the NR RLC device is afunction of sequentially transferring RLC SDUs, received from a lowerlayer, to a higher layer. If a single original RLC SDU is divided intomultiple RLC SDUs and the multiple RLC SDUs are received, thein-sequence delivery function may include a function of re-establishingand transferring the same. The in-sequence delivery function may includea function of reordering received RLC PDUs according to an RLC sequencenumber (SN) or a PDCP SN, a function of recording lost RLC PDUs aftersequential reordering, a function of reporting the states of lost RLCPDUs to a transmission side, a function of requesting retransmission oflost RLC PDUs, a function of sequentially transferring only RLC SDUsbefore a lost RLC SDU, to a higher layer, if a lost RLC SDU exists, or afunction of sequentially transferring all RLC SDUs, received before apredetermined timer starts, to a higher layer even though a lost RLC SDUexists, if the predetermined timer expires.

Alternatively, the in-sequence delivery function may include a functionof sequentially transferring all RLC SDUs, received up to the present,to a higher layer even though a lost RLC SDU exists, if a predeterminedtimer expires. Also, RLC PDUs are processed in order of reception (inorder of arrival, irrespective of a serial number or a sequence number),and are transmitted to the PDCP device irrespective of a sequence(out-of-sequence delivery). In the case of segments, segments, which arestored in a buffer or which are to be received in the future, arereceived and reconfigured as a single intact RLC PDU, are processed, andare transmitted to the PDCP device. The NR RLC layer may not include aconcatenation function. In addition, the concatenation function may beperformed in the NR MAC layer or may be replaced with a multiplexingfunction in the NR MAC layer.

The out-of-sequence delivery function of the NR RLC device is a functionof immediately transferring RLC SDUs, received from a lower layer, to ahigher layer irrespective of a sequence. If a single original RLC SDU isdivided into multiple RLC SDUs and the multiple RLC SDUs are received,the out-of-sequence delivery function may include a function ofre-establishing and transmitting the same, and a function of storing theRLC SN or PDCP SN of the received RLC PDUs, and performing sequentialordering, and recording lost RLC PDUs.

The NR MAC 2-15 and 2-30 may be connected to multiple NR RLC layersconfigured for a single UE, and the main functions of the NR MAC mayinclude some of the following functions:

-   -   Mapping (mapping between logical channels and transport        channels);    -   Multiplexing and demultiplexing (multiplexing/demultiplexing of        MAC SDUs);    -   Scheduling information reporting;    -   HARQ (error correcting through HARQ);    -   Priority handling between logical channels (priority handling        between logical channels of one UE);    -   Priority handling between UEs (priority handling between UEs by        means of dynamic scheduling);    -   MBMS service identification;    -   Transport format selection; and/or    -   Padding.

The NR PHY layer 2-20 and 2-25 performs channel-coding and modulating ofhigher layer data to generate an OFDM symbol and transmits the OFDMsymbol via a wireless channel, or performs demodulating andchannel-decoding of an OFDM symbol, received via a wireless channel, andtransmits the demodulated and channel-decoded OFDM symbol to a higherlayer.

FIG. 3 is a diagram illustrating technology that collects and reportscell measurement information according to an embodiment of the presentdisclosure.

To establish or optimize a network, a mobile communication operator maymeasure a signal strength in a generally estimated service area, andbased thereon, may dispose or readjust base stations in the servicearea. An operator may carry signal measurement equipment in a vehicle,and may collect cell measurement information in the service area, whichrequires a long time and high costs. The processor may be implementedgenerally using a vehicle, and is referred to as drive test 3-30. In thecase of inter-cell migration, in order to support operations such ascell reselection or handover (HO), serving cell addition, and the like,a UE may have a function of measuring a signal transmitted from a basestation, and reporting a measurement report. Therefore, instead of thedrive test, a UE 3-25 in the service area may be utilized, which isreferred to as minimization of drive test (MDT).

An operator may configure an MDT operation for predetermined UEs viavarious element devices 3-05, 3-10, and 3-15 of a network. The UEs maycollect signal strength information from a serving cell and neighborcells in an RRC connected mode (RRC_CONNECTED), an RRC idle mode(RRC_IDLE), or an RRC inactive mode (RRC_INACTIVE). In addition, the UEsmay store various types of information such as location information,time information, signal quality information, and the like. If the UEsare in a connected mode, the stored information may be reported to anetwork 3-15, and the information may be transferred to a predeterminedserver 3-20.

The operation of the MDT may be briefly classified as an immediate MDTand a logged MDT. Hereinafter, each will be described.

According to the immediate MDT, a UE directly reports collectedinformation to a network. Since the collected information needs to bedirectly reported, only a UE in an RRC connected mode is capable ofperforming the same. According to the immediate MDT, a radio resourcemanagement (RRM) measurement process to support operations such ashandover and service cell addition, and the like may be used, andlocation information, time information, and the like may be additionallyreported.

According to the logged MDT, a UE does not directly report collectedinformation to a network, and store the same, and the UE reports thestored information after the UE changes into an RRC connected mode. Thelogged MDT may be implemented by a UE in an RRC idle mode or a UE in anRRC inactive mode which is incapable of directly reporting the collectedinformation to a network. A UE in an RRC inactive mode which is employedin a next generation mobile communication system according to thedisclosure is capable of performing the logged MDT. If a predeterminedUE is in an RRC connected mode, the network may provide configurationinformation for performing logged MDT operation to the UE. The UE maychange into an RRC idle mode or an RRC inactive mode, may collect signalstrength information according to the configuration information, and maystore the same. In addition, the UE may collect and store various typesof information such as location information, time information, signalquality information, and the like, according to the configurationinformation. The RRC mode of a UE that performs immediate MDT and theRRC mode of a UE that performs logged MDT may be as shown in Table 1.

TABLE 1 RRC mode Immediate MDT RRC_CONNECTED Logged MDT RRC_IDLE,RRC_INACTIVE

FIG. 4 is a diagram illustrating a process in which a UE performshandover according to an embodiment of the present disclosure.

Particularly, 4 illustrates a process in which a UE successivelyperforms a mobility from evolved universal terrestrial radio access(E-UTRA) procedure, and moves to an NR cell according to an embodimentof the present disclosure.

Referring to FIG. 4, a UE 4-01 sets up (or establishes) an RRCconnection with an LTE base station 4-02, and may be in an RRC connectedmode (RRC_CONNECTED) in operation 4-05.

In operation 4-10, the UE 4-01 in the RRC connected mode may receive aLoggedMeasurementConfiguration message from the LTE base station 4-02.The message may include configuration information used for logging ameasurement result obtained in an RRC idle mode (RRC_IDLE) or an RRCinactive mode (RRC_INACTIVE) when the UE changes to the RRC idle mode orthe RRC inactive mode. If the UE 4-01 in the RRC connected mode receivesa LoggedMeasurementConfiguration message, the following exampleoperations may be performed.

In one example, if timer T330 is running, stop timer T330 (stop timerT330, if running).

In one example, if stored, delete logged measurement configurationstored in VarLogMeasConfig and logged measurement information stored inVarLogMeasReport (if stored, discard the logged measurementconfiguration as well as the logged measurement information, i.e.,release the UE variables VarLogMeasConfig and VarLogMeasReport).

In one example, if loggingDuration, loggingInterval, andareaConfiguration are included in the receivedLoggedMeasurementConfiguration message, store the same inVarLogMeasConfig (store the received loggingDuration, loggingIntervaland areaConfiguration, if included, in VarLogMeasConfig). For reference,loggingDuration may be a T330 timer value.

In one example, if the received LoggedMeasurementConfiguration messageincludes plmn-IdentityList, set a registered public land mobile network(RPLMN) and public land mobile networks (PLMNs) included in receivedplmn-IdentityList in plmn-IdentityList included in VarLogMeasReport (ifthe LoggedMeasurementConfiguration message includes plmn-IdentityList,set plmn-IdentityList in VarLogMeasReport to include the RPLMN as wellas the PLMNs included in plmn-IdentityList). If the receivedLoggedMeasurementConfiguration message does not includeplmn-IdentityList, set an RPLMN in plmn-IdentityList included inVarLogMeasReport (set plmn-IdentityList in VarLogMeasReport to includethe RPLMN).

In one example, store absoluteTimeInfo, traceReference,traceRecordingSessionRef, and tce-ID included in the receivedLoggedMeasurementConfiguration message in VarLogMeasReport (store thereceived absoluteTimeInfo, traceReference, traceRecordingSessionRef andtce-Id in VarLogMeasReport).

In one example, if the received LoggedMeasurementConfiguration messageincludes at least one of targetMBSFN-AreaList, bt-NameList, andwlan-NameList, store the same in VarLogMeasConfig (store the receivedtargetMBSFN-AreaList, if included, bt-NameList, if included,wlan-NameList, if included, in VarLogMeasConfig).

In one example, set a timer T330 value to a loggingDuration valueincluded in the received LoggedMeasurementConfiguration message, andoperate the timer T330 (start timer T330 with the timer value set to theloggingDuration).

The LoggedMeasurementConfiguration message may include an abstractsyntax notation one (ASN.1) structure as shown in Table 2.

TABLE 2 LoggedMeasurementConfiguration-r10 ::= SEQUENCE { criticalExtensions   CHOICE {   c1   CHOICE {loggedMeasurementConfiguration-r10 LoggedMeasurementConfiguration-r10-IEs, spare3 NULL, spare2 NULL, spare1 NULL   },   criticalExtensionsFuture   SEQUENCE { }  } }LoggedMeasurementConfiguration-r10-IEs ::= SEQUENCE { traceReference-r10  TraceReference-r10,  traceRecordingSessionRef-r10OCTET STRING (SIZE (2)),  tce-Id-r10   OCTET STRING (SIZE (1)), absoluteTimeInfo-r10 AbsoluteTimeInfo-r10,  areaConfiguration-r10AreaConfiguration-r10  OPTIONAL, -- Need OR  loggingDuration-r10 LoggingDuration-r10,  loggingInterval-r10  LoggingInterval-r10, nonCriticalExtension  LoggedMeasurementConfiguration-v1080-IEs OPTIONAL } LoggedMeasurementConfiguration-v1080-IEs ::= SEQUENCE { lateNonCriticalExtension-r10 OCTET STRING OPTIONAL, nonCriticalExtension  LoggedMeasurementConfiguration-v1130-IEs OPTIONAL } LoggedMeasurementConfiguration-v1130-IEs ::= SEQUENCE { plmn-IdentityList-r11 PLMN-IdentityList3-r11  OPTIONAL, -- Need OR areaConfiguration-v1130 AreaConfiguration-v1130  OPTIONAL, -- Need OR nonCriticalExtension  LoggedMeasurementConfiguration-v1250-IEs OPTIONAL } LoggedMeasurementConfiguration-v1250-IEs ::= SEQUENCE { targetMBSFN-AreaList-r12 TargetMBSFN-AreaList-r12  OPTIONAL, -- Need OP nonCriticalExtension  LoggedMeasurementConfiguration-v1530-IEs  OPTIONAL } LoggedMeasurementConfiguration-v1530-IEs ::= SEQUENCE { bt-NameList-r15  BT-NameList-r15 OPTIONAL,  --Need OR wlan-NameList-r15  WLAN-NameList-r15  OPTIONAL, --Need OR nonCriticalExtension SEQUENCE { }  OPTIONAL } TargetMBSFN-AreaList-r12::= SEQUENCE   (SIZE (0..maxMBSFN-Area)) OF TargetMBSFN-Area-r12TargetMBSFN-Area-r12 ::=  SEQUENCE {  mbsfn-AreaId-r12   MBSFN-AreaId-r12 OPTIONAL, -- Need OR  carrierFreq-r12   ARFCN- ValueEUTRA-r9, ... }

In operation 4-15, the LTE base station 4-02 may initiate a mobilityfrom E-UTRA procedure in order to handover the UE 4-01 in the RRCconnected mode to an NR cell. That is, the LTE base station 4-02 maytransmit a MobilityFromEUTRACommand message to the UE 4-01. If the UE4-01 receives the MobilityFromEUTRACommand message, the UE 4-01 mayperform the following example operations.

In one example, if timer T310 is running, stop timer T310 (stop timerT310, if running).

In one example, if timer T312 is running, stop timer T312 (stop timerT312, if running).

In one example, if timer T316 is running, stop timer T316 and clear allthe information included in VarRLF-Report (if timer T316 is running,stop timer T316 and clear the information included in VarRLF-Report, ifany).

In one example, if timer T309 is running, stop timer T309 for all accesscategories and perform operations specified TS 36.331 (if T309 isrunning, stop timer T309 for all access categories, and perform theactions as specified in TS 36.331).

-   -   In one example, if handover is set as a purpose and        targetRAT-Type is set to nr in the MobilityFromEUTRACommand        message (if the MobilityFromEUTRACommand message includes the        purpose set to handover and the targetRAT-Type is set to nr):    -   (1) aUE may regardthat inter-RAT mobility to NR is initiated        (consider inter-RAT mobility as initiated towards NR); or    -   (2) the UE may access a target cell 4-03 indicated in the        inter-RAT message according to TS 38.331 (access the target cell        indicated in the inter-RAT message in accordance with the        specification in TS 38.331).

The MobilityFromEUTRA message may have an ASN.1 structure as shown inTable 3.

TABLE 3 MobilityFromEUTRACommand ::= SEQUENCE { rrc-TransactionIdentifier RRC-TransactionIdentifier, criticalExtensions CHOICE {   c1   CHOICE{   mobilityFromEUTRACommand-r8  MobilityFromEUTRACommand-r8-IEs,   mobilityFromEUTRACommand-r9  MobilityFromEUTRACommand-r9-IEs,   spare2 NULL, spare1  NULL   },   criticalExtensionsFuture  SEQUENCE {}  } } MobilityFromEUTRACommand-r8-IEs ::= SEQUENCE { cs-FallbackIndicator  BOOLEAN,  purpose  CHOICE{   handover  Handover,  cellChangeOrder  CellChangeOrder  },  nonCriticalExtension MobilityFromEUTRACommand-v8a0-IEs OPTIONAL }MobilityFromEUTRACommand-v8a0-IEs ::= SEQUENCE { lateNonCriticalExtension OCTET STRING OPTIONAL,  nonCriticalExtension MobilityFromEUTRACommand-v8d0-IEs OPTIONAL }MobilityFromEUTRACommand-v8d0-IEs ::= SEQUENCE {  bandIndicator BandIndicatorGERAN OPTIONAL, --   Cond GERAN  nonCriticalExtension SEQUENCE { } OPTIONAL } MobilityFromEUTRACommand-r9-IEs ::= SEQUENCE { cs-FallbackIndicator  BOOLEAN,  purpose  CHOICE{   handover  Handover,  cellChangeOrder  CellChangeOrder,   e-CSFB-r9  E-CSFB-r9,   ...  }, nonCriticalExtension  MobilityFromEUTRACommand-v930-IEs OPTIONAL }MobilityFromEUTRACommand-v930-IEs ::= SEQUENCE { lateNonCriticalExtension OCTET STRING OPTIONAL,  nonCriticalExtension MobilityFromEUTRACommand-v960-IEs OPTIONAL }MobilityFromEUTRACommand-v960-IEs ::= SEQUENCE {  bandIndicator BandIndicatorGERAN  OPTIONAL,  -- Cond GERAN  nonCriticalExtension MobilityFromEUTRACommand-v1530-IEsOPTIONAL }MobilityFromEUTRACommand-v1530-IEs ::= SEQUENCE {  smtc-r15  MTC-SSB-NR-r15  OPTIONAL, -- Need OP  nonCriticalExtension  SEQUENCE { }OPTIONAL } Handover ::=  SEQUENCE {  targetRAT-Type  ENUMERATED {  utra, geran, cdma2000-1XRTT, cdma2000-HRPD,   nr, eutra, spare2, spare1, ...},  targetRAT-MessageContainer  OCTET STRING, nas-SecurityParamFromEUTRA  OCTET STRING (SIZE (1)) OPTIONAL,  -- CondUTRAGERANEPC  systemInformation SI-OrPSI- GERAN OPTIONAL -- Cond PSHO }CellChangeOrder ::= SEQUENCE {  t304  ENUMERATED {   ms100, ms200,ms500, ms1000,   ms2000, ms4000, ms8000, ms10000-V1310},  targetRAT-TypeCHOICE {    geran  SEQUENCE { physCellId   PhysCellIdGERAN, carrierFreq  CarrierFreqGERAN, networkControlOrder  BIT STRING (SIZE (2)) OPTIONAL,  -- Need OP systemInformation  SI-OrPSI-GERAN  OPTIONAL  --Need OP    },    ...  } } SI-OrPSI-GERAN ::=  CHOICE {  si SystemInfoListGERAN,  psi  SystemInfoListGERAN } E-CSFB-r9 ::= SEQUENCE {  messageContCDMA2000-1XRTT-r9  OCTET STRING  OPTIONAL,  --Need ON  mobilityCDMA2000-HRPD-r9  ENUMERATED {   handover, redirection} OPTIONAL, -- Need OP  messageContCDMA2000-HRPD-r9  OCTET STRING  OPTIONAL, -- Cond concHO  redirectCarrierCDMA2000-HRPD-r9CarrierFreqCDMA2000  OPTIONAL  -- Cond concRedir }

In operation 4-20, the UE 4-01 may successfully access the target cell4-03 and may successfully complete the mobility from an E-UTRA procedure(successful completion of the mobility from E-UTRA). That is, if the UE4-01 successfully completes handover to the target cell 4-03 (e.g., ifthe UE successfully completes a random access process procedure with atarget cell), and performs the following operations according to acondition, it is identified that the mobility from E-UTRA procedure issuccessfully completed.

In one example of Condition 1, a UE may be connected to a 5G corenetwork (5GC) before receiving MobilityFromEUTRACommand in operation4-15 (i.e., E-UTRA/5GC, E-UTRA connected to 5GC) in operation 4-15, andtargetRAT-Type may be set to nr in the received MobilityFromEUTRACommandmessage in operation 4-15.

In such example (e.g., action 1):

-   -   (1) the UE resets a MAC layer (reset MAC);    -   (2) the UE stops all timers that are currently running (stop all        timers that are running);    -   (3) if ran-NotificationAreaInfo is stored, the UE may release        ran-NotificationAreaInfo (release ran-NotificationAreaInfo, if        stored);    -   (4) if AS security context including KRRCenc key, KRRCint key,        KUPint key, and KUPenc key is stored, the UE may release all AS        security contexts including KRRCenc key, KRRCint key, KUPint        key, and KUPene key (release the AS security context including        the KRRCenc key, the KRRCint, the KUPint key and the KUPenc key,        if stored); and/or    -   (5) release all radio resources that may include an RLC entity,        MAC configuration, and a related PDCP entity and SDAP entity for        all established radio bearers (release all radio resources,        including release of the RLC entity, the MAC configuration and        the associated PDCP entity and SDAP entity for all established        RBs). In action 2 described below, PDCP and SDAP configurations        set in a source RAT before handover is performed may not be        released.

In one example of Condition 2, a UE may be connected to EPC beforereceiving MobilityFromEUTRACommand in operation 4-15 (i.e., E-UTRA/EPC),and targetRAT-Type may be set to nr in MobilityFromEUTRACommand messagereceived in 4-15.

In such example (e.g., action 2), the UE may perform an operation uponleaving RRC_CONNECTED as stated in TS 36.331 with release cause “other”(perform the action upon leaving RRC_CONNECTED as specified in TS 36.331with release cause “other”). In this instance, although timer T330 isrunning, the UE does not stop timer T330.

If condition 1 is satisfied and action 1 is performed, the UE accordingto an embodiment of the present disclosure may stop all timers that arerunning including timer T330. Therefore, if the NR cell 4-03 transmitsan RRC connection release message (RRCRelease) to the UE 4-01 inoperation 4-25, so as to shift (change) to an RRC idle mode (RRC_IDLE)or an RRC inactive mode (RRC_INACTIVE) in operation 4-30, the UE 4-01may not perform logging according to the LoggedMeasurementConfigurationmessage received in operation 4-10. Therefore, although an RRC idle modeor RRC inactive mode UE shifts to an RRC connected mode afterward, abase station may be incapable of receiving a measurement result that theUE logs from the UE, and thus, a network may be inefficiently operated,which is a drawback.

Conversely, in the case in which condition 2 is satisfied and action 2is performed, the UE may not stop if timer T330 is running. Therefore,if the NR cell 4-03 transmits an RRC connection release message(RRCRelease) to the UE 4-01 in operation 4-25, so as to shift (change)to an RRC idle mode (RRC_IDLE) or an RRC inactive mode (RRC_INACTIVE) inoperation 4-30, the UE 4-01 may perform logging according to theLoggedMeasurementConfiguration message received in operation 4-10.

In FIG. 4, operations 4-05 to 4-30 may be partially omitted or may beperformed in parallel.

FIG. 5 is a diagram illustrating a process in which a UE performshandover according to an embodiment of the present disclosure.

Particularly, FIG. 5 is a diagram illustrating a process in which a UEsuccessfully performs a mobility from E-UTRA procedure and moves to anNR cell according to an embodiment of the disclosure.

According to an embodiment of the disclosure, there is provided a methodin which a UE that successfully performs inter-RAT handover processestimer T330.

For example, if T330 timer is running, the UE that successfully performsinter-RAT handover may not stop timer T330 and may continuously operatetimer T330.

Referring to FIG. 5, the UE may establish an RRC connection to an LTEbase station, and may be in an RRC connected mode (RRC_CONNECTED) inoperation 5-05.

In operation 5-10, the UE may receive a LoggedMeasurementConfigurationmessage from the LTE base station.

In operation 5-15, the UE may set a T330 timer value to aloggingDuration value included in the LoggedMeasurementConfigurationmessage received in operation 5-10, and may operate timer T330.

In operation 5-20, the UE may receive a MobilityFromEUTRACommand messagefrom the LTE base station. The UE may identify that a purpose is set tohandover and targetRAT-Type is set to nr in the MobilityFromEUTRACommandmessage, and may identity that handover to an NR cell needs to beperformed.

In operation 5-25, the UE may successfully perform handover to the NRcell. For example, if a predetermined RRC message indicating that arandom access procedure with the NR cell is successfully performed orhandover to the NR cell is completed is transmitted, the UE maydetermine that the handover is successfully performed.

If the UE successfully completes handover to the NR cell, the UEdetermines whether the UE was connected to 5GC (E-UTRA/5GC) or wasconnected to an EPC (E-UTRA/EPC, E-UTRA connected to EPC) beforereceiving MobilityFromEUTRACommand in operation 5-20, in operation 5-30.

If the UE was connected to an EPC before receivingMobilityFromEUTRACommand, the UE may set an operation to be performedwhen leaving RRC_CONNECTED to release cause “other” as stated in TS36.331 in operation 5-35. In this instance, although timer T330 isrunning, the UE does not stop the same. Accordingly, although the UEthat sets up an RRC connection to the NR cell shifts to an RRC idle mode(RRC_IDLE) or an RRC inactive mode (RRC_INACTIVE) afterward, timer T330is continuously running, and thus the UE may perform a logging operationaccording to the LoggedMeasurementConfiguration message received inoperation 5-10.

If the UE was connected to 5GC before receivingMobilityFromEUTRACommand, the UE according to an embodiment of thedisclosure may stop the remaining timers excluding timer T330 among allthe timers that are currently running in operation 5-40. Although a UEstops timer T330 in action 1 in the above-described embodiment, a UE inthe embodiment does not stop but continuously operates timer T330 iftimer T330 is running in operation 5-40. Accordingly, although the RRCconnection to the NR cell to which handover is successfully performed isreleased and the UE shifts to an RRC idle mode (RRC_IDLE) or an RRCinactive mode (RRC_INACTIVE) afterward, timer T330 is continuouslyrunning, and thus the UE may perform a logging operation according tothe LoggedMeasurementConfiguration message received in operation 5-10.

In FIG. 5, operations 5-05 to 5-40 may be partially omitted or may beperformed in parallel.

FIG. 6 is a diagram illustrating a process in which a UE performshandover according to an embodiment of the present disclosure.

Particularly, FIG. 6 is a diagram illustrating a process in which a UEaccording to an embodiment of the disclosure successfully performs amobility from NR procedure and moves to a target cell.

Referring to FIG. 6, a UE 6-01 sets up (or establishes) an RRCconnection with an NR base station 6-02, and may be in an RRC connectedmode (RRC_CONNECTED) in operation 6-05.

In operation 6-10, the UE 6-01 in the RRC connected mode may receive aLoggedMeasurementConfiguration message from the NR base station 6-02.The message may include configuration information used for logging ameasurement result obtained in an RRC idle mode (RRC_IDLE) or an RRCinactive mode (RRC_INACTIVE) when the UE changes to the RRC idle mode orthe RRC inactive mode. If receiving the LoggedMeasurementConfigurationmessage, the UE 6-01 in the RRC connected mode may perform the followingexample operations.

In one example, if timer T330 is running, the UE stops timer T330 (stoptimer T330, if running).

In one example, if stored, the UE deletes logged measurementconfiguration stored in VarLogMeasConfig and logged measurementinformation stored in VarLogMeasReport (if stored, discard the loggedmeasurement configuration as well as the logged measurement information,i.e., release the UE variables VarLogMeasConfig and VarLogMeasReport).

In one example, if loggingDuration, reportType, and areaConfigurationare included in the received LoggedMeasurementConfiguration message, theUE stores the same in VarLogMeasConfig (store the receivedloggingDuration, reportType and areaConfiguration, if included, inVarLogMeasConfig). For reference, loggingDuration may be a T330 timervalue.

In one example, if the received LoggedMeasurementConfiguration messageincludes plmn-IdentityList, the UE sets an RPLMN and PLMNs included inthe received plmn-IdentityList in the plmn-IdentityList included inVarLogMeasReport (if the LoggedMeasurementConfiguration message includesplmn-IdentityList, set plmn-IdentityList in VarLogMeasReport to includethe RPLMN as well as the PLMNs included in plmn-IdentityList). If thereceived LoggedMeasurementConfiguration message does not includeplmn-IdentityList, set an RPLMN in plmn-IdentityList included inVarLogMeasReport (set plmn-IdentityList in VarLogMeasReport to includethe RPLMN).

In one example, the UE stores absoluteTimeInfo, traceReference,traceRecordingSessionRef, and tce-ID included in the receivedLoggedMeasurementConfiguration message in VarLogMeasReport (store thereceived absoluteTimeInfo, traceReference, traceRecordingSessionRef andtee-Id in VarLogMeasReport).

In one example, if the received LoggedMeasurementConfiguration messageincludes at least one of bt-NameList, wlan-NameList, or sensor-NameList,the UE stores the same in VarLogMeasConfig (store the receivedbt-NameList, if included, wlan-NameList, if included, sensor-NameList,if included, in VarLogMeasConfig).

In one example, set a T330 timer value to a loggingDuration valueincluded in the received LoggedMeasurementConfiguration message, and theUE may operate the timer T330 (start timer T330 with the timer value setto the loggingDuration).

The LoggedMeasurementConfiguration message may include an ASN.1structure as shown in Table 4.

TABLE 4 LoggedMeasurementConfiguration-r16 ::= SEQUENCE { criticalExtensions CHOICE {  loggedMeasurementConfiguration-r16  LoggedMeasurementConfiguration-r16-IEs,   criticalExtensionsFuture   SEQUENCE { }  } }LoggedMeasurementConfiguration-r16-IEs ::= SEQUENCE { traceReference-r16   TraceReference-r16,  traceRecordingSessionRef-r16   OCTET STRING (SIZE (2)),  tce-Id-r16 OCTET STRING (SIZE (1)), absoluteTimeInfo-r16   AbsoluteTimeInfo-r16,  areaConfiguration-r16  AreaConfiguration-r16 OPTIONAL, --Need R  plmn-IdentityList-r16  PLMN-IdentityList2-r16 OPTIONAL, --Need R  bt-NameList-r16SetupRelease {BT-NameList-r16} OPTIONAL, --Need M  wlan-NameList-r16    SetupRelease {WLAN-NameList-r16} OPTIONAL, --Need M sensor-NameList-r16     SetupRelease {Sensor-NameList-r16} OPTIONAL,--Need M  loggingDuration-r16   LoggingDuration-r16,  reportType  CHOICE{   periodical  LoggedPeriodicalReportConfig-r16,   eventTriggered  LoggedEventTriggerConfig-r16,   ...  },  lateNonCriticalExtension  OCTET STRING OPTIONAL,  nonCriticalExtension   SEQUENCE { } OPTIONAL }LoggedPeriodicalReportConfig-r16 ::=  SEQUENCE {  loggingInterval-r16   LoggingInterval-r16,  ... } LoggedEventTriggerConfig-r16::=  SEQUENCE {  eventType-r16   EventType-r16,  loggingInterval-r16   LoggingInterval-r16,  ... } EventType-r16 ::= CHOICE { outOfCoverage NULL,  eventL1  SEQUENCE {  l1-Threshold MeasTriggerQuantity,   hysteresis Hysteresis,  timeToTrigger TimeToTrigger  },  ... }

In operation 6-15, the NR base station 6-02 may initiate a mobility fromNR procedure in order to handover the UE 6-01 in an RRC connected modeto a target cell 6-03. Here, the target cell 6-03 may be at least one ofE-UTRA/EPC, E-UTRA/5GC, or universal terrestrial radio access-frequencydivision duplex (UTRA-FDD). The NR base station 6-02 may transmit aMobilityFromNRCommand message to the UE 6-01. If receiving theMobilityFromNRCommand message, the UE 6-01 may perform the followingexample operations.

In one example, if timer T310 is running, the UE stops timer T310 (stoptimer T330, if running).

In one example, if timer T312 is running, the UE stops timer T312 (stoptimer T312, if running).

In one example, if timer T316 is running, the UE stops timer T316 andcancels all the information included in VarRLF-Report (if timer T316 isrunning, stop timer T316 and clear the information included inVarRLF-Report, if any).

In one example, if timer T309 is running, the UE stops timer T309 forall access categories and perform operations specified in TS 38.331 (ifT309 is running, stop timer T309 for all access categories, and performthe actions as specified in TS 38.331).

In one example, if targetRAT-Type is set to eutra (if the targetRAT-Typeis set to eutra):

-   -   (1) a UE may regard that inter-RAT mobility to E-UTRA is        initiated (consider inter-RAT mobility as initiated towards        E-UTRA); and/or    -   (2) If nas-SecurityParamFromNR is included, the UE forwards the        same to a higher layer (forward the nas-SecurityParamFromNR to        the upper layers, if included).

In one example, if targetRAT-Type is set to utra-fdd (if thetargerRAT-Type is set to utra-fdd):

-   -   (1) a UE may regard that inter-RAT mobility to UTRA-FDD is        initiated (consider inter-RAT mobility as initiated towards        UTRA-FDD); and/or    -   (2) if nas-SecurityParamFromNR is included, the UE forwards the        same to a higher layer (forward the nas-SecurityParamFromNR to        the upper layers, if included).

The MobilityFromNR message may have an ASN.1 structure as shown in Table5.

TABLE 5 MobilityFromNRCommand ::=   SEQUENCE { rrc-TransactionIdentifier  RRC-TransactionIdentifier, criticalExtensions CHOICE {  mobilityFromNRCommand   MobilityFromNRCommand-IEs,  criticalExtensionsFuture    SEQUENCE { }  } }MobilityFromNRCommand-IEs ::=   SEQUENCE {  targetRAT-Type   ENUMERATED{ eutra, utra-fdd-v1610, spare2, spare1, ...}, targetRAT-MessageContainer   OCTET STRING,  nas-SecurityParamFromNR OCTET STRING OPTIONAL, -- CondHO-ToEPCUTRAN  lateNonCriticalExtension OCTET STRING OPTIONAL,  nonCriticalExtension    MobilityFromNRCommand-v1610-IEs OPTIONAL }MobilityFromNRCommand-v1610-IEs ::= SEQUENCE { voiceFallbackIndication-r16 ENUMERATED {true} OPTIONAL, -- Need N nonCriticalExtension SEQUENCE { }   OPTIONAL }

In operation 6-20, the UE 6-01 may successfully access the target cell6-03 and may successfully complete the mobility from NR procedure(successful completion of the mobility from NR). That is, if the UE 6-01successfully completes handover to the target cell 6-03 (e.g., if the UEsuccessfully completes a random access process procedure with the targetcell), and performs the following example operations at the source side,it is identified that the mobility from NR procedure is successfullycompleted.

In one example, the UE resets a MAC layer (reset MAC).

In one example, the UE stops the remaining timers excluding timer T400and timer T330 among all timer that are currently running (stop alltimers that are running except T330 and T400). In an embodiment of thedisclosure, the UE does not stop timer T330.

In one example, if ran-NotificationAreaInfo is stored, the UE mayrelease the ran-NotificationAreaInfo (release ran-NotificationAreaInfo,if stored).

In one example, if AS security context including KRRCenc key, KRRCintkey, KUPint key, and KUPenc key is stored, the UE may release all ASsecurity contexts including KRRCenc key, KRRCint key, KUPint key, andKUPenc key (release the AS security context including the KRRCenc key,the KRRCint, the KUPint key and the KUPenc key, if stored).

In one example, the UE may clear a PDCP entity and an SDAP entity forall established radio resources (release the associated PDCP entity andSDAP entity for all established RBs). For reference, PDCP and SDAPconfigurations set in a source RAT before HO is performed may not bereleased.

In one example, if a targetRAT-Type is set to utra-fdd or targerRAT-Typeis set to eutra, and nas-SecurityParamFromNR is included, the UEreports, to higher layers, that RRC connection is released together withrelease cause “other” (if the targetRAT-Type is set to utra-fdd or ifthe targetRAT-Type is set to eutra and the nas-SecurityParamFromNR isincluded, indicate the release of the RRC connection to upper layerstogether with the release cause “other”).

In FIG. 6, operations 6-05 to 6-20 may be partially omitted or may beperformed in parallel.

According to above-described embodiments, if a UE successfully completesinter-RAT handover (including handover from an LTE base station to an NRcell or handover from an NR cell to a target cell), the UE does not stopbut continuously operate timer T330. Accordingly, although the UE shiftsto an RRC idle mode or an RRC inactive mode, the UE may perform alogging operation according to a LoggedMeasurementConfiguration messagereceived from the base station.

If the UE fails to perform an inter-RAT handover or an intra-RAThandover, the UE may determine the content of a radio link failure (RLF)report. For example, the UE may store handover failure information inthe content of the RLF report. Hereinafter, detailed descriptionsthereof will be provided with reference to FIG. 7.

FIG. 7 is a diagram illustrating a process of storing handover failureinformation when a UE fails to perform handover according to anembodiment of the present disclosure.

Referring to FIG. 7, the UE may establish an RRC connection to an NRbase station, and may be in an RRC connected mode (RRC_CONNECTED) inoperation 7-05.

In operation 7-10, the UE may receive an RRCReconfiguration messageincluding reconfigurationWithSync from the NR base station.

In operation 7-15, the ULE may operate timer T304 for a correspondingSpCell using a t304 timer value included in reconfigurationWithSync(start timer T304 for the corresponding SpCell with the timer value setto t304, as included in the reconfigurationWithSync). If frequencyInfoDLis included in reconfigurationWithSync, a cell on a synchronizationsignal block (SSB) frequency indicated by frequencyinfoDL with aphysical cell identity indicated by physCellId may be regarded as atarget SpCell (if the frequencyInfoDL is included, consider the targetSpCell to be one on the SSB frequency indicated by the frequencyInfoDLwith a physical cell identity indicated by the physCellId). Otherwise(if frequencyInfoDL is not included in reconfigurationWithSync), a cellon an SSB frequency of a source SpCell with a physical cell identityindicated by physCellId may be regarded as a target SpCell (else,consider the target SpCell to be one on the SSB frequency of the sourceSpCell with a physical cell identity indicated by the physCellId).

In operation 7-20, the UE successfully may perform a reconfigurationwith sync (i.e., handover) and may transmit anRRCReconfigurationComplete message to the target SpCell.

In operation 7-23, the UE may receive a handover command (HO Command)from the NR base station.

If the UE determines that the HO command received in operation 7-23 isRRCReconfiguration including reconfigurationWithSync in operation 7-25,the UE may operate timer T304 for the corresponding SpCell using a t304timer value included in reconfigurationWithSync in operation 7-30.

In operation 7-35, the UE may identify that intra-RAT handover (handoverfrom an NR cell to the NR cell) fails due to a predetermined reason. Thepredetermined reason may be the case in which timer T304 operated inoperation 7-30 expires.

In operation 7-40, the UE may store handover failure information inVarRLF-Report. The UE may perform action 3 described below and may storehandover failure information in VarRLF-Report.

In one example (e.g., Action 3):

-   -   (1) the UE deletes information in VarRLF-Report (clear the        information included in VarRLF-Report, if any);    -   (2) the UE sets plmn-IdentityList to include the list of stored        EPLMNs and RPLM (set the plmn-IdentityList to include the list        of EPLMNs stored by the UE (i.e., includes the RPLMN));    -   (3) the UE stores measurement values of a source PCell and        measurement values of neighboring cells;    -   (4) the UE sets c-RNTI to C-RNTI used in the source PCell (set        the c-RNTI to the C-RNTI used in the source PCell (in case HO        failure));    -   (5) the UE sets connectionFailureType to hof,    -   (6) the UE sets nrFailedPCellId in failedPCellId to a global        cell identity and tracing area code, if available, and        otherwise, set nrFailedPCellId in failedPCellId to the physical        cell identity and the carrier frequency of a target PCell to        which handover fails (set the nrFailedPCellId in failedPCellId        to the global cell identity and tracking area code, if        available, and otherwise to the physical cell identity and        carrier frequency of the target PCell of the failed handover);    -   (7) the UE sets nrPreviousCell of previousPCellId to the global        cell identity and tracking area code of the PCell that transmits        the HO command message (RRCReconfiguration including        reconfigurationWithSync) in operation 7-23 (include        nrPreviousCell in previousPCellId and set it to the global cell        identity and tracking area code of the PCell where the last        RRCReconfiguration message including reconfigurationWithSync was        received) In the disclosure, a global cell identity refers to        the following:    -   (8) the UE sets timeConnFailure to the period of time elapsing        from the point in time of reception of the HO command message        (i.e., RRCReconfiguration including reconfigurationWithSync)        received in operation 7-23 (set the timeConnFailure to the        elapsed time since reception of the last RRCReconfiguration        message including the reconfigurationWithSync);    -   (9) the UE includes information related to random access in        ra-InformationCommon In this instance, information related to        random access may be included in ra-InformationCommon according        to TS 38.331, and for example, ra-InformationCommon may have a        structure as shown in Table 7:

TABLE 7 RA-InformationCommon-r16 ::=   SEQUENCE { absoluteFrequencyPointA-r16   ARFCN-ValueNR,  locationAndBandwidth-r16  INTEGER (0..37949),  subcarrierSpacing-r16  SubcarrierSpacing, msg1-FrequencyStart-r16  INTEGER (0..maxNrofPhysicalResourceBlocks-1) OPTIONAL,  msg1-FrequencyStartCFRA-r16   INTEGER(0..maxNrofPhysicalResourceBlocks−1) OPTIONAL, msg1-SubcarrierSpacing-r16  SubcarrierSpacing  OPTIONAL, msg1-SubcarrierSpacingCFRA-r16 SubcarrierSpacing OPTIONAL, msg1-FDM-r16   ENUMERATED {one, two, four, eight} OPTIONAL, msg1-FDMCFRA-r16   ENUMERATED {one, two, four, eight} OPTIONAL, perRAInfoList-r16 PerRAInfoList-r16 };

-   -   (10) if location information is present, the UE sets contents of        locationInfo.

If the UE determines that the HO Command received in operation 7-23 isMobilityFromNRCommand in operation 7-25, the UE may operate timer T304using a t304 timer value included in mobilityControlInfo in operation7-45.

In operation 7-50, the UE may identify that inter-RAT handover (handoverfrom an NR cell to an E-UTRA cell) fails due to a predetermined reason.

In operation 7-55, the UE may determine whether the inter-RAT handoverfailure (i.e., mobility from NR failure) in operation 7-50 is caused dueto failure of connection to target radio access technology.

If it is determined that the mobility from NR failure occurs sinceconnection to the target radio access technology fails in operation7-55, and a radio link failure report is supported for inter-RATmobility robustness optimization (MRO) EUTRA, the UE may store handoverfailure information in VarRLF-Report in operation 7-60. The UE mayperform action 4 described below and may store handover failureinformation in VarRLF-Report.

In one example (e.g., Action 4):

-   -   (1) the UE deletes information in VarRLF-Report (clear the        information included in VarRLF-Report, if any);    -   (2) the UE sets plmn-IdentityList to include the list of stored        EPLMNs and an RPLM (set the plmn-IdentityList to include the        list of EPLMNs stored by the UE (i.e., includes the RPLMN));    -   (3) the UE stores measurement values of a source PCell and        measurement values of neighboring cells;    -   (4) the UE sets c-RNTI to C-RNTI used in the source PCell (set        the c-RNTI to the C-RNTI used in the source PCell (in case HO        failure));    -   (5) the UE sets connectionFailureType to hof;    -   (6) the UE sets eutraFailedPCellId in failedPCellId to a global        cell identity and tracing area code, if available, and        otherwise, set eutraFailedPCellId in failedPCellId to the        physical cell identity and the carrier frequency of a target        PCell to which handover fails (set the eutraFailedPCellId in        failedPCellId to the global cell identity and tracking area        code, if available, and otherwise to the physical cell identity        and carrier frequency of the target PCell of the failed        handover). For reference, in the disclosure, a global cell        identity refers to the following:    -   (7) the UE sets nrPreviousCell of previousPCellId to the global        cell identity and tracking area code of the PCell that transmits        the HO command message (RRCReconfiguration including        reconfigurationWithSync) in operation 7-10 (include        nrPreviousCell in previousPCellId and set it to the global cell        identity and tracking area code of the PCell where the last        RRCReconfiguration message including reconfigurationWithSync was        received);    -   (8) the UE sets timeConnFailure to the period of time elapsing        from the point in time of reception of the HO command message        (i.e., RRCReconfiguration including reconfigurationWithSync)        received in operation 7-10 (set the timeConnFailure to the        elapsed time since reception of the last RRCReconfiguration        message including the reconfigurationWithSync); and/or    -   (9) the UE includes information related to random access in        ra-InformationCommon In this instance, information related to        random access may be included in ra-InformationCommon according        to TS 38.331, and for example, ra-InformationCommon may have a        structure as shown in Table 9.

TABLE 9 RA-InformationCommon-r16 ::=   SEQUENCE { absoluteFrequencyPointA-r16   ARFCN-ValueNR,  locationAndBandwidth-r16  INTEGER (0..37949),  subcarrierSpacing-r16  SubcarrierSpacing, msg1-FrequencyStart-r16  INTEGER (0..maxNrofPhysicalResourceBlocks−1) OPTIONAL,  msg1-FrequencyStartCFRA-r16   INTEGER(0..maxNrofPhysicalResourceBlocks−1) OPTIONAL, msg1-SubcarrierSpacing-r16  SubcarrierSpacing  OPTIONAL, msg1-SubcarrierSpacingCFRA-r16 SubcarrierSpacing OPTIONAL, msg1-FDM-r16   ENUMERATED {one, two, four, eight} OPTIONAL, msg1-FDMCFRA-r16   ENUMERATED {one, two, four, eight} OPTIONAL, perRAInfoList-r16 PerRAInfoList-r16 }

In the disclosure, supporting a radio link failure report for inter-RATMRO EUTRA may refer to the following.

TABLE 10 Radio Link Failure Report for inter-RAT MRO EUTRA Indicateswhether the UE supports: Include EUTRA CGI and associated TAC, ifavailable, and otherwise to include the physical cell identity andcarrier frequency of the target PCell of the failed handover asfailedPCellId in RLF-Report upon request from the network as specifiedin TS 38.331. Include EUTRA CGI and associated TAC as previousPCellId inRLF-Report as specified in TS 38.331. Include eutraReconnectCellId inreconnectCellId in the RLF-Report as specified in TS 38.331 upon UE hasradio link failure or handover failure and successfully re-connected toan E-UTRA cell.

If the above described action 4 is performed, nrPreviousCell ofpreviousPCellId may be set to the global identity and tracking area codeof the PCell that transmits the HO command message (RRCReconfigurationincluding reconfigurationWithSync) in operation 7-10 and may be storedin VarRLF-Report, and this may be different from the PCell in operation7-23. Since the UE performs handover in operation 7-10, 7-15, and 7-20,and thus, the PCell in operation 7-10 and the PCell in operation 7-23may be different PCells.

In addition, timeConnFailure may be set to the period of time elapsingfrom the point in time of reception of the HO command message(RRCReconfiguration including reconfigurationWithSync) in operation 7-10and may be stored in VarRLF-Report. Accordingly, timeConnFailure may beset to a longer period of time than the period of time actually elapsingfrom the reception of the HO command message in operation 7-23. In thisinstance, wrong time information may be reported to a base station. Inaddition, ra-InformationCommon which is information related to randomaccess may be information related to random access to an NR cell. The UEperforms random access to E-UTRA cell via handover, and thus the UE mayset ra-InformationCommon to wrong information or random information.

If mobility from NR failure occurs not by the failure of connection totarget radio access technology in operation 7-55, but occurs due to thefollowing condition, the UE may not store handover failure informationin VarRLF-Report in operation 7-65.

Condition:

-   -   (1) if the UE is incapable of complying with configuration        included in MobilityFromNRCommand (UE is unable to comply with        any part of the configuration included in the        MobilityFromNRCommand) or    -   (2) if a protocol error occurs in inter RAT information included        in MobilityFromNRCommand, and the UE fails a procedure according        to the specification applicable to a target RAT (there is a        protocol error in the inter RAT information included in the        MobilityFromNRCommand message, causing the UE to fail the        procedure according to the specification applicable for the        target RAT).

In FIG. 7, operations 7-05 to 7-65 may be partially omitted or may beperformed in parallel.

If mobility from NR failure occurs due to the condition, the UE may notstore handover failure information in VarRLF-Report, and afterward, abase station occasionally fails to collect handover failure information.

Therefore, there is desire for a method of storing handover failureinformation although the UE fails to perform handover due to theabove-described condition, and the method will be described in detailwith reference to FIG. 8.

FIG. 8 is a diagram illustrating a process of storing handover failureinformation when a UE fails to perform handover according to anembodiment of the present disclosure.

Referring to FIG. 8, the UE may establish an RRC connection to an NRbase station, and may be in an RRC connected mode (RRC_CONNECTED) inoperation 8-05.

In operation 8-10, the UE may receive an RRCReconfiguration messageincluding reconfigurationWithSync from the NR base station.

In operation 8-15, the UE may operate a timer T304 for a correspondingSpCell using a t304 timer value included in reconfigurationWithSync(start timer T304 for the corresponding SpCell with the timer value setto t304, as included in the reconfigurationWithSync). If frequencyInfoDLis included in reconfigurationWithSync, a cell on an SSB frequencyindicated by frequencyinfoDL with a physical cell identity indicated byphysCellId may be regarded as a target SpCell (if the frequencyInfoDL isincluded, consider the target SpCell to be one on the SSB frequencyindicated by the frequencyInfoDL with a physical cell identity indicatedby the physCellId). Otherwise (if frequencyInfoDL is not included inreconfigurationWithSync), a cell on an SSB frequency of a source SpCellwith a physical cell identity indicated by physCellId may be regarded asa target SpCell (else, consider the target SpCell to be one on the SSBfrequency of the source SpCell with a physical cell identity indicatedby the physCellId).

In operation 8-20, the UE successfully performs reconfiguration withsync (i.e., handover) and may transmit an RRCReconfigurationCompletemessage to the target SpCell.

In operation 8-23, the UE may receive a HO command from the NR basestation.

In operation 8-25, if the UE determines that the HO Command received inoperation 8-23 is RRCReconfiguration including reconfigurationWithSync,the UE may operate a timer T304 for the corresponding SpCell using at304 timer value included in reconfigurationWithSync in operation 8-30.

In operation 8-35, the UE may identify that intra-RAT handover (handoverfrom an NR cell to the NR cell) fails due to a predetermined reason. Thepredetermined reason may be the case in which timer T304 operated inoperation 8-30 expires.

In operation 8-40, the UE may store handover failure information inVarRLF-Report. The UE may perform above-described action 3 and may storehandover failure information in VarRLF-Report.

In operation 8-25, if the UE determines that the HO Command received inoperation 8-23 is MobilityFromNRCommand, the UE may operate timer T304using a t304 timer value included in mobilityControlInfo in operation8-45.

In operation 8-50, the UE may identify that inter-RAT handover (handoverfrom an NR cell to an E-UTRA cell, mobility from NR failure) fails dueto a predetermined reason. If mobility from NR failure occurs due to atleast one of the following conditions, the UE according to an embodimentof the disclosure may perform operation 8-55.

Condition:

-   -   (1) if a UE fails to connect to a target radio access technology        (UE does not succeed in establishing the connection to the        target radio access technology);    -   (2) if the UE is incapable of complying with configuration        included in MobilityFromNRCommand (UE is unable to comply with        any part of the configuration included in the        MobilityFromNRCommand); or    -   (3) if a protocol error occurs in inter RAT information included        in MobilityFromNRCommand, and the UE fails a procedure according        to the specification applicable to a target RAT (there is a        protocol error in the inter RAT information included in the        MobilityFromNRCommand message, causing the UE to fail the        procedure according to the specification applicable for the        target RAT).

In operation 8-55, if the UE supports a radio link failure report forinter-RAT MRO EUTRA and the MobilityFromNRCommand message received inoperation 8-25 corresponds to inter-RAT handover failure from NR toE-UTRA (MobilityFromNRCommand concerned a failed inter-RAT handover fromNR to E-UTRA and the UE supports radio link failure report for Inter-RATMRO EUTRA), the UE may store handover failure information inVarRLF-Report. The UE may perform action 4 described below and may storehandover failure information in VarRLF-Report.

Modified action 4:

-   -   (1) the UE deletes information in VarRLF-Report (clear the        information included in VarRLF-Report, if any);    -   (2) the UE sets plmn-IdentityList to include the list of stored        EPLMNs and an RPLM (set the plmn-IdentityList to include the        list of EPLMNs stored by the UE (i.e., includes the RPLMN));    -   (3) the UE stores measurement values of a source PCell and        measurement values of neighboring cells;    -   (4) the UE sets c-RNTI to C-RNTI used in the source PCell (set        the c-RNTI to the C-RNTI used in the source PCell (in case HO        failure));    -   (5) the UE sets connectionFailureType to hof,    -   (6) the UE sets eutraFailedPCellId in failedPCellId to a global        cell identity and tracing area code, if available, and        otherwise, set eutraFailedPCellId in failedPCellId to the        physical cell identity and the carrier frequency of a target        PCell to which handover fails (set the eutraFailedPCellId in        failedPCellId to the global cell identity and tracking area        code, if available, and otherwise to the physical cell identity        and carrier frequency of the target PCell of the failed        handover);    -   (7) the UE sets nrPreviousCell of previousPCellId to the global        cell identity and tracking area code of the PCell of the HO        command message (i.e., MobilityFromNRCommand) received in        operation 8-23 and include the same (include nrPreviousCell in        previousPCellId and set it to the global cell identity and        tracking area code of the PCell where the last        MobilityFromNRCommand message was received);    -   (8) the UE sets timeConnFailure to the period of time elapsing        from the point in time of reception of the HO command message        (i.e., MobilityFromNRCommand) received in operation 8-23 (set        the timeConnFailure to the elapsed time since reception of the        last MobilityFromNRCommand); and/or    -   (9) the UE does not include the same in ra-InformationCommon.        Alternatively, include at least one of the following random        access information in VarRLF-Report:    -   (i) ARFCN-ValueEUTRA;    -   (ii) information associated with contention based random access        resource or information associated with contention free random        access resource; and    -   (iii) following information or information list in chronological        order    -   (a) the number of times that random access is continuously        attempted;    -   (b) whether contention detection occurs;    -   (c) whether rsrp-Threshold exceeds in the case of transmission        of a preamble; and/or    -   (d) a cause of performing random access.

Operations 8-30 to 8-40 of FIG. 8 are the same as the descriptions whichhave been described above, and will be omitted herein.

In FIG. 8, operations 8-05 to 8-55 may be partially omitted or may beperformed in parallel.

FIG. 9 is a diagram illustrating a process of storing handover failureinformation when a UE fails to perform handover according to anembodiment of the present disclosure.

Referring to FIG. 9, the UE may set up an RRC connection to an LTE basestation, and may be in an RRC connected mode (RRC_CONNECTED) inoperation 9-05.

In operation 9-10, the UE may receive an RRCConnectionReconfigurationmessage including mobilityControlInfo from the LTE base station.

In operation 9-15, the UE may operate timer T304 using a t304 timervalue included in mobilityControlInfo (start timer T304 with the timervalue set to t304, as included in the mobilityControlInfo).

In operation 9-20, the UE may successfully perform handover and maytransmit an RRCConnectionReconfigurationComplete message to a targetPCell.

In operation 9-25, the UE may receive a MobilityFromEUTRACommand messagefrom the LTE base station. The UE may identify that a purpose is set tohandover and targetRAT-Type is set to nr in the receivedMobilityFromEUTRACommand message.

In operation 9-30, the UE may identify that inter-RAT handover (handoverfrom an E-UTRA cell to an NR cell) fails due to a predetermined reason.The predetermined reason may be at least one of the following examples.

In one example, whether the UE fails to connect to a target radio accesstechnology (UE does not succeed in establishing the connection to thetarget radio access technology).

In one example, whether the UE is incapable of complying with aconfiguration included in MobilityFromEUTRACommand (UE is unable tocomply with any part of the configuration included in theMobilityFromEUTRACommand).

In one example, whether a protocol error occurs in inter RAT informationincluded in MobilityFromEUTRACommand, and the UE fails a procedureaccording to the specification applicable to a target RAT (there is aprotocol error in the inter RAT information included in theMobilityFromEUTRACommand message, causing the UE to fail the procedureaccording to the specification applicable for the target RAT).

In operation 9-35, if the UE supports a radio link failure report forinter-RAT MRO NR and the MobilityFromEUTRACommand message received inoperation 9-25 corresponds to inter-RAT handover failure from EUTRA toNR (MobilityFromEUTRACommand concerned a failed inter-RAT handover fromE-UTRA to NR and the UE supports radio link failure report for Inter-RATMRO NR), the UE may store handover failure information in VarRLF-Report.The UE may perform action 5 described below and may store handoverfailure information in VarRLF-Report.

In one example (e.g., Action 5):

-   -   (1) the UE deletes information in VarRLF-Report (clear the        information included in VarRLF-Report, if any);    -   (2) the UE sets plmn-IdentityList to include the list of stored        EPLMNs and an RPLM (set the plmn-IdentityList to include the        list of EPLMNs stored by the UE (i.e., includes the RPLMN));    -   (3) the UE stores measurement values of a source PCell and        measurement values of neighboring cells;    -   (4) the UE sets failedNR-PCellId to a global cell identity and        tracing area code, and otherwise, sets failedNR-PCellId to the        physical cell identity and the carrier frequency of a target        PCell to which handover fails (set the failedNR-PCellId to the        global cell identity and tracking area code, if available, and        otherwise to the physical cell identity and carrier frequency of        the target PCell of the failed handover);    -   (5) the UE sets PreviousCellID to the global cell identity and        tracking area code of the PCell of MobilityFromEUTRACommand        received in operation 9-25 and includes the same (include        previousPCellId and set it to the global cell identity and        tracking area code of the PCell where the last        MobilityFromEUTRACommand message was received);    -   (6) the UE sets timeConnFailure to the period of time elapsing        from the point in time of reception of MobilityFromEUTRACommand        received in operation 9-25 (set the timeConnFailure to the        elapsed time since reception of the last        MobilityFromEUTRACommand);    -   (7) the UE sets c-RNTI to C-RNTI used in the source PCell (set        the c-RNTI to the C-RNTI used in the source PCell (in case HO        failure));    -   (8) the UE sets connectionFailureType to hof; and/or    -   (9) the UE includes information related to random access in        ra-InformationCommon In this instance, information related to        random access may be included in ra-InformationCommon according        to TS 38.331, and for example, ra-InformationCommon may have a        structure as shown in Table 11.

TABLE 11 RA-InformationCommon-r16 ::=   SEQUENCE { absoluteFrequencyPointA-r16   ARFCN-ValueNR,  locationAndBandwidth-r16  INTEGER (0..37949),  subcarrierSpacing-r16  SubcarrierSpacing, msg1-FrequencyStart-r16  INTEGER (0..maxNrofPhysicalResourceBlocks−1) OPTIONAL,  msg1-FrequencyStartCFRA-r16   INTEGER(0..maxNrofPhysicalResourceBlocks−1) OPTIONAL, msg1-SubcarrierSpacing-r16  SubcarrierSpacing  OPTIONAL, msg1-SubcarrierSpacingCFRA-r16 SubcarrierSpacing OPTIONAL, msg1-FDM-r16   ENUMERATED {one, two, four, eight} OPTIONAL, msg1-FDMCFRA-r16   ENUMERATED {one, two, four, eight} OPTIONAL, perRAInfoList-r16 PerRAInfoList-r16 }

In the disclosure, supporting a radio link failure report for inter-RATMRO NR may refer to the following.

TABLE 12 It is optional for UE to include previousNR-PCellId,failedNR-PCellId and nrReconnectCellId in RLF-Report upon request fromthe network as specified in TS 36.331.

In FIG. 9, operations 9-05 to 9-35 may be partially omitted or may beperformed in parallel.

FIG. 10 is a block diagram illustrating the structure of a UE accordingto an embodiment of the present disclosure.

Referring to FIG. 10, the UE includes a radio frequency (RF) processor10-10, a baseband processor 10-20, a storage 10-30, and a controller10-40. The controller 10-40 includes a multi-access processor 10-42.

The RF processor 10-10 performs a function for transmitting or receivinga signal via a wireless channel, such as band conversion andamplification of a signal. That is, the RF processor 10-10 up-converts abaseband signal provided from the baseband processor 10-20 into an RFband signal so as to transmit the RF band signal via an antenna, anddown-converts an RF band signal received via the antenna into a basebandsignal.

For example, the RF processor 10-10 may include a transmission filter, areception filter, an amplifier, a mixer, an oscillator, adigital-to-analog converter (DAC), an analog-to-digital converter (ADC),and the like. Although only a single antenna is illustrated in thedrawing, the UE may include a plurality of antennas. In addition, the RFprocessor 10-10 may include a plurality of RF chains. Moreover, the RFprocessor 10-10 may perform beamforming. For the beamforming, the RFprocessor 10-10 may control the phase and the size of each of thesignals transmitted or received via a plurality of antennas or antennaelements. In addition, the RF processor may perform MIMO, and mayreceive multiple layers when performing a MIMO operation.

The baseband processor 10-20 performs a function of converting between abaseband signal and a bitstream according to the physical layer standardof a system. For example, in the case of data transmission, the basebandprocessor 10-20 encodes and modulates a transmission bitstream, so as toproduce complex symbols. In addition, in the case of data reception, thebaseband processor 10-20, restores a reception bitstream by demodulatingand decoding a baseband signal provided from the RF processor 10-10.

For example, according to an orthogonal frequency division multiplexing(OFDM) scheme, in the case of data transmission, the baseband processor10-20 produces complex symbols by encoding and modulating a transmissionbitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols via an inverse fast Fourier transform (IFFT) operation andcyclic prefix (CP) insertion. Further, in the case of data reception,the baseband processor 10-20 divides the baseband signal provided fromthe RF processor 10-10 in units of OFDM symbols, reconstructs thesignals mapped to the subcarriers via a fast Fourier transform (FFT)operation, and then reconstructs a received bitstream via demodulationand decoding.

The baseband processor 10-20 and the RF processor 10-10 transmit andreceive signals as described above. Accordingly, the baseband processor10-20 and the RF processor 10-10 may be referred to as a transmitter, areceiver, a transceiver, or a communication unit. Furthermore, at leastone of the baseband processor 10-20 and the RF processor 10-10 mayinclude a plurality of communication modules in order to supportdifferent multiple radio access technologies. In addition, at least oneof the baseband processor 10-20 and the RF processor 10-10 may includedifferent communication modules to process signals of differentfrequency bands. For example, the different radio access technologiesmay include a wireless LAN (e.g., IEEE 802.11), a cellular network(e.g., LTE), and the like. In addition, the different frequency bandsmay include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band and amillimeter wave (mm wave) (e.g., 60 GHz) band.

The storage 10-30 may store data such as a basic program, an applicationprogram, and configuration information for the operation of the UE.Particularly, the storage 10-30 may store information related to asecond access node that performs wireless communication using a secondradio access technology. In addition, the storage 10-30 provides datastored therein in response to a request from the controller 10-40.

The controller 10-40 controls overall operation of the UE. For example,the controller 10-40 may perform transmission or reception of a signalvia the baseband processor 10-20 and the RF processor 10-10. Inaddition, the controller 10-40 may record data in the storage 10-40 andread the data. To this end, the controller 10-40 may include at leastone processor. For example, the controller 10-40 may include acommunication processor (CP) that performs control for communication,and an application processor (AP) that controls a higher layer such asan application program.

FIG. 11 is a block diagram illustrating the structure of a base stationaccording to an embodiment of the present disclosure.

Referring to FIG. 11, the base station may include an RF processor11-10, a baseband processor 11-20, a backhaul communication unit 11-30,a storage 11-40, and a controller 11-50.

The RF processor 11-10 performs a function for transmitting or receivinga signal via a wireless channel, such as band conversion andamplification of a signal. That is, the RF processor 11-10 up-converts abaseband signal provided from the baseband processor 11-20 into an RFband signal so as to transmit the RF band signal via an antenna, anddown-converts an RF band signal received via the antenna into a basebandsignal.

For example, the RF processor 11-10 may include a transmission filter, areception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC,and the like. Although only a single antenna is illustrated in thedrawing, a plurality of antennas may be included. In addition, the RFprocessor 11-10 may include a plurality of RF chains. In addition, theRF processor 11-10 may perform beamforming. For the beamforming, the RFprocessor 11-10 may control the phase and the size of each of thesignals transmitted or received via a plurality of antennas or antennaelements. The RF processor may perform a downlink MIMO operation bytransmitting one or more layers.

The baseband processor 11-20 performs a function of conversion between abaseband signal and a bitstream according to the physical layerstandard. For example, in the case of data transmission, the basebandprocessor 11-20 encodes and modulates a transmission bitstream, so as toproduce complex symbols. In addition, in the case of data reception, thebaseband processor 11-20, restores a reception bitstream by demodulatingand decoding a baseband signal provided from the RF processor 11-10.

For example, according to the OFDM scheme, in the case of datatransmission, the baseband processor 11-20 may produce complex symbolsby encoding and modulating a transmission bitstream, map the complexsymbols to subcarriers, and then configure OFDM symbols via an IFFToperation and CP insertion. In addition, in the case of data reception,the baseband processor 11-20 divides a baseband signal provided from theRF processor 11-10 in units of OFDM symbols, restores signals mappedonto the subcarriers via the FFT operation, and restores a received bitstream via demodulation and decoding. The baseband processor 11-20 andthe RF processor 11-10 transmit and receive signals as described above.Accordingly, the baseband processor 11-20 and the RF processor 11-10 maybe referred to as a transmitter, a receiver, a transceiver, acommunication unit, or a wireless communication unit.

The backhaul communication unit 11-30 may provide an interface forperforming the communication with other nodes in a network. That is, thebackhaul communication unit 11-30 may convert, into a physical signal, abit stream transmitted from the primary base station to another node,for example, a secondary base station, a core network, and the like, andmay convert a physical signal received from the other node into a bitstream.

The storage 11-40 stores data such as a basic program, an applicationprogram, and configuration information for the operation of the primarybase station. Particularly, the storage 11-40 may store informationassociated with a bearer allocated to a connected UE, a measurementresult reported from a connected UE, and the like. In addition, thestorage 11-40 may provide multiple accesses to a UE, or may storeinformation which is a criterion for determining whether to disconnectthe access. In addition, the storage unit 11-40 provides data storedtherein according to a request of the controller 11-50.

The controller 11-50 may control the overall operation of the primarybase station. For example, the controller 11-50 may transmit or receivea signal via the baseband processor 11-20 and the RF processor 11-10, orvia the backhaul communication unit 11-30. In addition, the controller11-50 may record data in the storage 11-40 and read the data. To thisend, the controller 11-50 may include at least one processor.

The embodiments of the disclosure described and shown in thespecification and the drawings are merely specific examples that havebeen presented to easily explain the technical contents of thedisclosure and help understanding of the disclosure, and are notintended to limit the scope of the disclosure. That is, it will beapparent to those skilled in the art that other variants based on thetechnical idea of the disclosure may be implemented. Further, one ormore of the above embodiments may be employed in combination, asnecessary.

Although specific embodiments have been described in the detaileddescription of the disclosure, various modifications and changes may bemade thereto without departing from the scope of the disclosure.Therefore, the scope of the disclosure should not be defined as beinglimited to the embodiments, but should be defined by the appended claimsand equivalents thereof.

In addition, the methods described in FIGS. 1 to 11 of the disclosuremay include methods based on combinations of at least one of thedrawings according to various implementation. For example, FIGS. 1 to 11may be combined to be performed as one sequence. The disclosure mayinclude methods based on combinations of at least one drawings accordingto various implementation.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method performed by a user equipment (UE) in acommunication system, the method comprising: receiving, from a basestation associated with new radio-radio access (NR), a command messagefor inter-radio access technology (RAT) handover from the NR to a targetRAT, wherein the command message includes information on a type of thetarget RAT; performing a procedure associated with the inter-RAThandover based on the command message; in case that a failure conditionfor the inter-RAT handover is satisfied, identifying that the inter-RAThandover fails; and in case that the type of the target RAT is set toevolved universal terrestrial radio access (EUTRA) and the UE supports aradio link failure report for inter-RAT mobility robustness optimization(MRO) EUTRA, storing handover failure information in a variable for theradio link failure report based on an identification that the inter-RAThandover fails.
 2. The method of claim 1, wherein the failure conditionfor the inter-RAT handover is satisfied when: the UE does not succeed inestablishing a connection to the target RAT; the UE is unable to complywith any part of a configuration included in the command message; or aprotocol error occurs in inter-RAT information included in the commandmessage, the protocol error causing the UE to fail a procedureapplicable for the target RAT.
 3. The method of claim 1, wherein storingthe handover failure information comprises: including NR previous cellinformation in previous cell identifier (ID) information of the variablefor the radio link failure report; and setting the NR previous cellinformation to a global cell identity and a tracking area code of aprimary cell (PCell) where the command message was received.
 4. Themethod of claim 1, wherein storing the handover failure informationcomprises: setting time connection failure information of the variablefor the radio link failure report to an elapsed time since reception ofthe command message.
 5. The method of claim 1, wherein storing thehandover failure information comprises: in case that the command messageis associated with the failed inter-RAT handover from the NR to theEUTRA and the UE supports the radio link failure report for theinter-RAT MRO EUTRA, setting EUTRA failed primary cell (PCell)identifier (ID) information of the variable for the radio link failurereport to a global cell identity and a tracking area code.
 6. The methodof claim 1, wherein storing the handover failure information comprises:in case that the command message is associated with the failed inter-RAThandover from the NR to the EUTRA and the UE supports the radio linkfailure report for the inter-RAT MRO EUTRA, setting EUTRA failed primarycell (PCell) identifier (ID) information of the variable for the radiolink failure report to a physical cell identity and a carrier frequencyof a target PCell of the failed inter-RAT handover.
 7. The method ofclaim 1, further comprising: in case that the inter-RAT handover issuccessfully completed, skipping stopping a timer associated with loggedmeasurement.
 8. The method of claim 1, further comprising: in case thatconnection failure type information of the variable for the radio linkfailure report is set to a handover failure and a failed handover is anintra-RAT handover, setting common random-access related information ofthe variable for the radio link failure report to include random-accessrelated information used in a random access procedure.
 9. A userequipment (UE) in a communication system, the UE comprising: atransceiver; and a controller operably coupled to the transceiver, thecontroller configured to: receive, from a base station associated withnew radio-radio access (NR) via the transceiver, a command message forinter-radio access technology (RAT) handover from the NR to a targetRAT, wherein the command message includes information on a type of thetarget RAT, perform a procedure associated with the inter-RAT handoverbased on the command message, in case that a failure condition for theinter-RAT handover is satisfied, identify that the inter-RAT handoverfails, and in case that the type of the target RAT is set to evolveduniversal terrestrial radio access (EUTRA) and the UE supports a radiolink failure report for inter-RAT mobility robustness optimization (MRO)EUTRA, store handover failure information in a variable for the radiolink failure report based on an identification that the inter-RAThandover fails.
 10. The UE of claim 9, wherein the failure condition forthe inter-RAT handover is satisfied when: the UE does not succeed inestablishing a connection to the target RAT; the UE is unable to complywith any part of a configuration included in the command message; or aprotocol error occurs in inter-RAT information included in the commandmessage, the protocol error causing the UE to fail a procedureapplicable for the target RAT.
 11. The UE of claim 9, wherein thecontroller is configured to: include NR previous cell information inprevious cell identifier (ID) information of the variable for the radiolink failure report, and set the NR previous cell information to aglobal cell identity and a tracking area code of a primary cell (PCell)where the command message was received.
 12. The UE of claim 9, whereinthe controller is configured to: set time connection failure informationof the variable for the radio link failure report to an elapsed timesince reception of the command message.
 13. The UE of claim 9, whereinthe controller is configured to: in case that the command message isassociated with the failed inter-RAT handover from the NR to the EUTRAand the UE supports the radio link failure report for the inter-RAT MROEUTRA, set EUTRA failed primary cell (PCell) identifier (ID) informationof the variable for the radio link failure report to a global cellidentity and a tracking area code.
 14. The UE of claim 9, wherein thecontroller is configured to: in case that the command message isassociated with the failed inter-RAT handover from the NR to the EUTRAand the UE supports the radio link failure report for the inter-RAT MROEUTRA, set EUTRA failed primary cell (PCell) identifier (ID) informationof the variable for the radio link failure report to a physical cellidentity and a carrier frequency of a target PCell of the failedinter-RAT handover.
 15. The UE of claim 9, wherein the controller isfurther configured to: in case that the inter-RAT handover issuccessfully completed, skip stopping a timer associated with loggedmeasurement.
 16. The UE of claim 9, wherein the controller is furtherconfigured to: in case that connection failure type information of thevariable for the radio link failure report is set to a handover failureand a failed handover is an intra-RAT handover, set common random-accessrelated information of the variable for the radio link failure report toinclude random-access related information used in a random accessprocedure.